The present invention relates generally to view-finders for television cameras, and more particularly to a view-finder in which an optical black and white or monochrome image from a monochrome image picture receiving device is superimposed thereon an optical color image made by light diverged from a light path from an object to be image-picked up to an image pick-up device in a television camera. The composite image formed by the superimposed images is observed in a view-finder by an operator in operating the television camera.
When the operator picks up images by means of a television camera, he usually uses the view-finder of the television camera in order to adjust the focus of the lens of the television camera and to decide the angle of view or view angle of the television camera.
Conventional known view-finders include electronic type view-finders and optical type view-finders.
The known electronic type view-finder has a Braun tube or cathode-ray tube (hereinafter referred to as a CRT) provided in the view-finder housing. The CRT is supplied with an output signal of an image pick-up tube of the television camera. The operator of the television camera adjusts the focus and decides the view angle of the television camera as he observes the picture screen of the CRT in the view-finder.
In this known electronic type view-finder, the sharpness of the edges of the image is improved by supplying the output video signal from the image pick-up tube to an aperture correction circuit (where the output signal is processed electrically. Accordingly, the operator can adjust the focus easily and precisely as he observes the picture screen in the view-finder. Besides, when the output video signal of the image pick-up tube is supplied to a magnetic video signal recording and/or reproducing apparatus (so-called video tape recorder. It is referred to as a VTR hereinafter.) and recorded on a magnetic tape therein, the CRT of the view-finder may be supplied with a video signal sent back from the VTR. In this case, the CRT of the viewfinder is used as a monitor television picture receiver for the VTR, since the operator of the television camera and VTR can recognize the recording condition of the VTR as he observes the received picture image.
However, when a color CRT is employed instead of the monochrome CRT, the electronic type view-finder disadvantages inevitably gives rise to such as which increase in manufacturing cost of the view-finder, increase in electric power consumption, and increase in weight of the view-finder. Accordingly, especially in a portable or simple type television camera, when the cost, electric power consumption and weight factors are taken into consideration, the monochrome CRT should be used for the CRT of the view-finder even in a color television camera.
When the operator adjusts and decides the view angle of the color television camera for the object to be image-picked up, he adjusts the direction of the television camera and the state of zooming of the zoom lens thereof taking the color of the object into consideration. At that time, it is therefore difficult for him to decide the view angle, since the image in the view-finder is not color but monochrome. More exactly, since he can not recognize the color of the object from the monochrome image picture in the view-finder, he has to take his eye off the view-finder and then to turn his eyes to the real object to recognize the color thereof and decide the approximate view angle. Thereafter, he observes the monochrome picture screen in the view-finder. He repeats the above operations and decides the view angle. Accordingly, the operation for deciding the view angle is very troublesome.
On the other hand, the known optical type view-finder is so designed that a light diverged from a light path from an afocal lens system to an image pick-up tube is introduced into the view-finder. The operator of the television camera observes the optical image formed by focusing the diverged light by lenses.
The known optical type view-finder has an advantage in that the operator can easily decide the view angle of the television camera as he observes the color image picture in the view-finder. Since the optical type view-finder does not employ a CRT, it has further advantages in that electric power is not used and the view-finder is light in weight.
However, the optical type view-finder has a disadvantage in that the operator can not adjust precisely the focus of the televison camera, since the image in the view-finder is an optical one and therefore his eyes focus naturally--that is, unconsciously. There have been optical type view-finders in which the optical image is projected onto a frosted glass or prism plate. The operator observes the projected image through a lens. In this case, his unconscious adjusting of focus is prevented. However, in this view-finder the image is dark, so it is difficult for the operator to adjust the focus precisely. Anyway, the optical type view-finder has the disadvantage that it is difficult to adjust the focus precisely. Furthermore, since the optical type view-finder has no CRT, it is impossible to monitor the video signal from the VTR.